Protective coating

ABSTRACT

A coating composition comprises an aqueous solution of lithium sodium silicate (see Division C1), 2-4 parts of a metallic dust, e.g. Zn of particle size 3-25 microns, and an alkali metal dichromate, e.g. 0.05-10%, optionally together with sand or silica gel, other finely divided metals, e.g. Al or Mg, metal oxides, e.g. Mn, Fe, or Ti, and 0.01-20% alkali metal or ammonium borate or bicarbonate.  The Li-Na silicate solution, either alone, or with the addition of 5-80% of a filler, e.g. casein, clay, sugars, aluminiates, or asbestos, and 0.01-3% of a curing agent, e.g. KCl, KBr, or borax, may be used as an adhesive or cement for wood, paper (Example 11), cardboard (Example 10), plastics, glass (Example 7), metals, concrete, or brick. Specification 1,007,482 is referred to.ALSO:Metal surfaces are coated with a composition containing an aqueous solution of lithium sodium silicate (see Division C1) together with (a) an inert filler, e.g. asbestos, or pigments, and 50-100 parts of an emulsified polymer per 5-50 parts silicate, or (b) 2-4 parts of a metallic dust, e.g. Zn of particle size 3-25 microns and an alkali metal dichromate, e.g. 0.05-0.1%, optionally together with sand or silica gel, other finely divided metals, e.g. Al or Mg, metal oxides, e.g. Mn, Fe, or Ti, or 0.01-20% alkali metal or ammonium borate or bicarbonate.  In Examples 12 and 14 a composition containing polyvinyl acetate or butyl rubber with iron oxide and talc is used to coat steel.  In Examples 15-21 a composition containing Zn dust and K dichromate is used to protect steel from contact with water or hydrocarbons. Specification 1,007,482 is referred to.ALSO:A composition containing an aqueous solution of lithium sodium silicate (see Division C1) mixed with glass fibres, asbestos fibres, paper fibres, or sawdust, is applied as a coating by trowel (see Examples 8 and 9).  An emulsified polymer such as polyvinyl acetate or chloride or butyl rubber may be incorporated into the aqueous solution of lithium sodium silicate together with inert fillers, e.g. asbestos or pigments.  50-100 parts polymer are used per 5-50 parts silicate.  The composition may be applied to metal, concrete, brick or plaster by brush, roller or spray. Examples 12 and 14 relate to the use of polyvinyl acetate or butyl rubber with iron oxide and talc.  Specification 1,007,482 is referred to.ALSO:An aqueous solution of lithium sodium silicate, in which the molar amounts of Li2O1Na2O, and SiO2 are 0.75-1, 0.05-0.25, and 2.5-5.0 respectively, is prepared by mixing LiOH, NaOH, silicic acid or silica gel, and water, heating at 75-250 DEG  C., and cooling to 20-30 DEG  C.  The rate of cooling is preferably decreased after 95 DEG  C.  The solution may contain 10-45% of the Li-Na silicate. Specification 1,007,482 is referred to.ALSO:An aqueous solution of lithium sodium silicate [see Division C1] is used to impregnate cotton fabric and paper (Ex. 2) and asbestos (Ex. 3), or as an adhesive for sticking pieces of cardboard together (Ex. 10).  A dye may be incorporated (Ex. 4). The solution may be applied by spray, brush, roller, or dipping, under pressure or vacuum and dried by evaporation.  It is said to render the material resistant to fire, water, wear, weather high temperatures, and biological decomposition. Glass fibres may be bound using the aqueous solution of lithium sodium silicate (see Ex. 7).  Specification 1,007,482 is referred to.ALSO:An aqueous solution of lithium sodium silicate (see Division C1) is used to coat asbestos fibres (Example 8), paper fibres (Example 9), saw-dust, wood, plastics, glass, metals, concrete or brick.  The solution may contain 5-80% fillers, e.g. casein, clay, sugars, aluminates, or asbestos, and 0,01-3% curing agents, e.g. KCl, KBr, or borax.  It may be applied by brush, dip, roller, or spray. The Li-Na silicate solution may contain 2-4 parts of a metallic dust, e.g. Zn of particle size 3-25 microns, and an alkali metal dichromate, e.g. 0,05-0,10%, optionally together with sand or silicon gel, other finely divided metals, e.g. Al or Mg, metal oxides, e.g. Mn, Fe, or Ti, and o,01-20% alkali metal or ammonium borate or bicarbonate; and is used to protect metal surfaces in contact with water or hydrocarbons.  Examples 15-21 relate to coating steel, e.g. a sandblasted steel panel, with a Li-Na silicate solution containing Zn dust and K dichromate.  Specification 1,007,482 is referred to.ALSO:An aqueous solution of lithium sodium silicate (see Division C1) is used to protect wood e.g. pine, oak, and fir, against rot, termites and wood borers (see Example 5).  The coating may be applied by spray, brush, roller, or dipping, under pressure or vacuum, and is dried by evaporation.  Specification 1,007,482 is referred to.

' few- 3,180,746 PKOTECTIVE COATING Robert H. Patton, Baytown, James B.Cox, Pasadena, and

Wesley K. Stich, Jr., Houston, Tex., assignors, by mesne assignments, toEsso Research and Engineering Company, Elizabeth, N.J., a corporation ofDelaware No Drawing. Filed Aug. 3, 1961, Ser. No. 128,963

28 Claims. (Cl. 106-74) enemies -protective, insulating, bonding, etc.,coating.

The present invention may be briefly described as a single-applicationliquid coating composition which comprises an aqueous solution of amixture of lithium and sodium silicate, the lithium and sodium silicatesbeing employed in amounts sufficient to provide a ratio of lithium oxideto sodium oxide to silicon dioxide, respectively, within the range fromabout 0.75 to about 1.00:about 0.05 to about 0.25zabout 2.5 to about5.0. In its more specific aspects, the invention is concerned with theaddition of certain additives to the lithium-sodium silicate solution toprovide specially adapted coating materials.

The lithium-sodium silicate solution of the present invention has beenfound to have numerous uses when used alone or when additives arecombined with the lithiumsodium silicate solution for specific purposes.The s qlp tign of the present invention when used alone may be "appliedby brush, spray or dipping and renders flexible materials such as paperor fabric into a rigid form having moisture resistant andmnonflamrna'bleproperties. Materials which are rigid can besealed against the passageof moisture and made fireproof by the solution of the present invention.Also, the solution of the present invention can be colored with stabledyes to impart desirable colors. When applied to either a flexible orrigid material, the solution of the present invention impregnates thematerial with a protective coating to a greater extent than knownsilicate solutions having comparable molar concentration because of thelower viscosity of the solution of the present invention. Thep'fbtective coating is strong, moistu resistant, fire r sistant, and hasa \lmffigiltyffigfmmdfthe-mmas been effective not only against Water andfire, but provides protection from such things as abrasion, wear,weather, high temperatures, biological decomposition, etc. The solutionwhen applied to a material dries rapidly and when dried, surprisinglyresults in an insoluble coating.

The solution of the present invention is also capable of lendingstrength to wood as well as protection against rot, fire, waterabsorption, and may also be effective against termites, wood borers andother destructive insects. Further, the solution of the presentinvention is capable of bonding, waterproofing and general strengtheningof glass matting, asbestos, paper, cloth and similar materials. Thesolution may be sprayed, brushed, rolled or mopped on surfaces such asinsulation, paper, cardboard, and similar materials, or generally asurface of such a nature which may be impregnated with the solution.Still further, the solution of the present invention has been found tobe a new and useful surface bonding, adhesive and cementing agent.

The present invention is still further directed to a single-applicationcoating material wherein the solution of the present invention is usedas a liquid vehicle to which is mixed inert fillers such as asbestos,dye and/or 3,180,746 I Patented Apr. 27, 1965 colored pigments, andemulsified polymers such as vinyl acetate and butyl rubber. The coatingof the present invention which incorporates the polymers and inertfillers and pigments is suitable for coating metal, concrete, brick,plaster, and similar materials. The resulting coating is inexpensive,nonflammable, odorless and easy to apply by brush, roller or spray. Theresulting film imparts color, corrosion protection, and seals thesurface against the passage of moisture. The alkaline nature of theconcrete, plaster, etc., does not afiect the coatings durability nor itsability to provide a water resistant protective coating. Thus, theprotective coating of the present invention has application in coatingconcrete piping, coloring and sealing concrete blocks, plaster andbricks, marking highways, runways and parking areas, protection of metalsurfaces, decorative coating for concrete floors, and generalmaintenance painting.

Surprisingly, it has been found that the incorporation of a dispersionof a metallic dust in the lithium-sodium silicate solution of thepresent invention, the lithium-sodium silicate solution being used as aliquid vehicle, with a small but effective amount of an alkaline metaldichromate provides a useful and important protective coating formetallic surfaces such as storage tanks for crude petroleum andfractions thereof such as gasoline, kerosene, gas oil, diesel oil,heating and lubricating oils, etc. The coating composition may also beemployed to protect ships bottoms and the interior of ships, tanks andthe like, providing protection from corrosion without contamination ofhydrocarbons, aqueous solutions, and the like contained in the tanks.

The present invention is also concerned with a method of preparing thelithium-sodium silicate solution in which lithium hydroxide which ispreferably the monohydrate since it is easier to use and commerciallyavailable, sodium hydroxide and silica containing materials such assilieic acid and silica gel, are added to water while agitating same,following which the admixture is heated while continuing the agitationthereof to a temperature within the range from about to about C. for asufiicient length of time to form a mixture of lithium and sodiumsilicates. The sodium and lithium hydroxide and silica containingmaterial are used in amounts sufficient to provide a ratio of lithiumoxide to sodium oxide to silicon dioxide within the range from about0.75 to about 1.00zabout 0.05 to about 0.25zabout 2.5 to about 5.0,respectively, following which the admixture is cooled to a temperaturewithin the range from about 20 to about 30 C. at which temperature anysolids go into solution and form an aqueous solution thereof.

The invention will be further illustrated by the following specificexamples which are given by way of illustration and not as limitationson the scope of the invention.

One aspect of the present invention is the making and use of thelithium-sodium silicate solution without the addition of any additivematerials. The composition in accordance with this aspect of theinvention was made up in the following manner:

EXAMPLE 1 Water, silica gel, lithium hydroxide, and sodium hydroxide arecharged into a stainless steel pressure vessel equipped with anagitator. During the initial mixing of these ingredients, evolution ofheat raises the temperature of the contents to 50-55 C. The reactor isthen sealed and the temperature of the reactants, under continualagitation, is raised to 150 C. over a period of time, which may varyfrom thirty to ninety minutes. After the vessel reaches about 150 C. andabout 70 pounds per square inch of pressure, the contents are slowlycooled at a rate of about 061 C. to about 1.83 C. per minute. This willresult in a temperature drop from 150 C. to about 95 C. within aboutthirty to about ninety minutes. This completes the initial part of thereaction which forms the solid sodium lithium silicate.

The second part of the operation (below 95 C.) requires a longer periodof time in order to effectively dissolve the solid silicate at lowertemperatures. The reduction of the temperature of the reactor contentsfrom 95 C. to 40 C. at a rate of about 0.37 C. to about 0.146 C. perminute should be accomplished within 150 minutes to 240 minutes. Thelast temperature drop from 40 C. to 25 C. may be conducted over a periodof 60 to 120 minutes at a cooling rate of about 0.25 C. to about 0.125C. per minute.

Depending upon the amount of water used, the solution may be used indifferent solids ratios, i.e., the total solids of the solution may varyfrom about to 45% by weight.

EXAMPLE 2 A solution was prepared in a manner similarly as described inExample 1 except that it was made from the following ingredients:

Grams Sodium hydroxide Lithium hydroxide monohydrate 62 Silica gel 300Water 1146 This solution can be described as (0.75 Li O+0.25 Na O) :5SiO with a total solids content of about Cloth fabric and paper weresaturated with this aqueous solution and allowed to air dry. Afterdrying they were rigid, fireproof, and withstood 72 hours exposure to100% relative humidity at 40 C.

EXAMPLE 3 A solution identical to Example 2 was used as an adhesivebinder for asbestos. The resulting composition was moisture resistantand fireproof. The composition was heated under an open flame for 3hours and then inserted directly into cold water without affecting thecohesion of the material.

EXAMPLE 5 A solution from Example 2 was used to seal preformed asbestosinsulation against the passage of moisture. The solution was coloredwith a stable red dye in order to produce a colored seal coating. After120 hours exposure to 100% relative humidity at 40 C., the solutionexhibited excellent waterproofing properties.

From the foregoing examples it can be seen that the resultinglithium-sodium silicate composition of the present invention is moistureresistant and fireproof when applied by brush, spray or dipping topaper, fabric, cardboard, wallboard and similar materials. The solutionof the present invention is prepared having a total solids content ofbetween about 10% and about by weight for the foregoing purposes.

The solution of the present invention may be used to protect wood whenthe total solids of the solution varies from about 10% to 35% by weightas shown by the following examples:

EXAMPLE 6 These chemicals were placed into a stainless steel pressurevessel under continual agitation. The temperature was raised to 150 C.;then the temperature was gradually reduced to 25 C. over an eight hourperiod in a manner similar to Example 1.

EXAMPLE 7 Grams Compound (of Example 6) 500.0 Water 100.0

This mixture was placed into a container and three types of wood (pine,oak, fir) were immersed for 30 minutes under a constant pressure of 25mm./Hg. The wooden panels were removed and dried thoroughly, thensubjected to an open flame. The wood was charred but at no time did itburn. A microscopic examination revealed that approximately 60% of thevoids in the wood were occupied by silica.

From the foregoing example it can be seen that the solution of thepresent invention is capable of lending strength to wood as well asprotection against rot, fire, and water absorption, etc.

The solution of the present invention rather than being applied as afilm may be applied by mixing the lithium-- sodium silicate solution ina matrix such as glass fibers, asbestos, paper fibers, saw dust, andsimilar materials, and applied to a material as a protective coatingdirectly by trowel. When mixed in a matrix of material the solution ofthe present invention has a solids content of about 10% to 35% byweight. It has been found that the solution of the present inventionwhether applied as a film or mixed in a matrix is completely waterinsoluble when cured and is unaffected by most chemicals with theexception of hydrogen fluoride and strong concentrated alkalies. Theeffectiveness of the nonflammable, odorless, nontoxic solution is shownby the following examples.

EXAMPLE 8 Grams Lithium hydroxide monohydrate 62.0 Sodium hydroxide 20.0Silica gel 270.0 Water 952.0

These chemicals were placed into a stainless steel pressure vessel undercontinual agitation. The tempera ture was raised to 150 C.; then thetemperature was gradually reduced to 25 C. over an 8 hour period in amanner similar to Example 1.

EXAMPLE 9 (1) Solution of Example 825% solids (2) 30 02. glass mattingThe glass matting was dipped in the solution and allowed to air dry at25 C. for 2 hours. The matting was then subjected to elevatedtemperatures and exhibited rigidity and superior binding qualities attemperatures nearing the melting point of glass.

EXAMPLE 10 (1) Solution of Example 825% solids (2) 24 oz. woven ravingThe solution was applied to the roving with a brush and allowed to airdry for 2 hours at 25 C. The roving exhibited rigidity and wasunaffected by an open flame and water.

EXAMPLE 11 (1) Solution of Example 825% solids (2) Asbestos The solutionwas mixed with asbestos fibers and applied by brush to a sandblastedfurnace stack at approximately C. The asbestos and lithium-sodiumsilicate solution exhibited excellent adhesion and good insulativequalities.

EXAMPLE 12 (1) Solution of Example 825% solids (2) Paper fibers Thepaper fibers were dispersed in the solution and applied by hand to asteam line exposed to the weather. After 60 days exposure there was novisible deterioration and excellent adhesion as well as insulativequalities were observed.

EXAMPLE 13 (1) Solution of Example 8--25% solids (2) Preformed pipeinsulation The solution was sprayed onto new preformed pipe coveringexposed to natural weathering and tested for 60 days; no visibledeterioration was evident and the insulation appeared to be waterinsensitive.

EXAMPLE 14 (1) Solution of Example 825% solids (2) Cardboard Thecardboard was dipped in the solution and allowed to air dry at 25 C. for4 hours. The cardboard exhibited excellent Water insensitivity andrigidity.

Another unique feature of the present invention is that thelithium-sodium silicate solution may be used as a surface bonding,adhesive, and cementing agent. The surface bonding agent of the presentinvention is use ful in the bonding of two or more surfaces to produce astrong, water resistant bond. In particular, the bonding agent of thepresent invention can be used for a large variety of surfaces such as:wood, paper, cardboard, cloth, plastics, glass, metal, concrete, brick,etc. As a new and useful surface bonding, adhesive, and cementing agent,the lithium-sodium silicate solution of the present invention can beused by itself or in admixture with various additives. Two classes ofadditives have been found to be the most effective. Materials such ascasein, clay, sugars, aluminates, asbestos, and organic materials act asfillers whereas materials such as borax, potassium chloride, andpotassium bromide act as curing agents to enhance the rate ofpolymerization of the silicate solution during air drying. The additivesare mixed with the solution of the present invention in amounts suchthat the total additives make up between about 0.0% and 85% by weight ofthe mixed solution. However, of the additives the filler material isused in the range of about 0.0% to about 80% by weight of the mixedsolution and preferably between about 5% and about 80% by Weight,whereas the curing agents are used in amounts within the range of about0.01% to about 5.0% by weight, preferably 0.01% to 3.0% by weight of themixed solution. The addition of the additives to the solution improvesthe quality of bonding obtained in a specific application. A preferredadhesive composition comprises adding to the lithium-sodium silicatesolution of the present invention clay as a filler material in an amountof about 5% to about 20% by weight of the composition and borax as acuring agent in an amount of about 0.2% by weight of the composition.

It has been found that the mixed lithium-sodium silicate solution of thepresent invention, when applied to a surface and allowed to dry, has amuch smaller porosity than other silicate solutions, and hence, thebonding, adhesive, and cementing characteristics of the presentinvention are greater than other known silicates.

The following examples are given as illustrations of the bonding,adhesive and cementing characteristics of the present invention:

EXAMPLE 15 The lithium-sodium silicate solution, identical incomposition to that described in Example 2, was applied to the surfaceof two pieces of ordinary, brown cardboard.

6 The two pieces of cardboard were then pressed together and held underpressure in a vise and allowed to dry for 24 hours. The resultingbonding was excellent as evidenced by the fact that upon pulling the twopieces apart, the paper fibers were pulled apart rather than aseparation occurring at the original interface.

EXAMPLE 16 In another experiment, an adhesive mixture was prepared bythoroughly mixing parts of the lithiumsodium silicate solution ofExample 2 with 20 parts of dry powdered clay. A small double layer pieceof cheese cloth was dipped into this mixture and placed between twopieces of brown paper and pressed together in a vise for a period of twohours. The sample was then removed and allowed to dry for an additionalhour. The resulting bonding was stronger than the paper itself.

Another aspect of the present invention is a water soluble coating whichwill dry by water evaporation into a water and hydrocarbon resistantfilm composition for metal, concrete, brick, plaster and similarmaterials which are of such a nature as to be impregnated with thesoluble coating. The soluble coating is obtained by using thelithium-sodium silicate solution of the present invention as a liquidvehicle and adding thereto a mixture of inert fillers such as asbestos,dye and/ or colored pigments and emulsified polymers such as vinylacetate and butyl rubber. The addition of the dye or colored pigments isan optional feature; however, the addition of color to the coatingenhances the appearance of the coating composition and therefore findsutility in many more instances. The best general coating compositionillustrating this aspect of the invention can be described by thegeneral formula A (polymer) +B [(C Li O+D Na O) :E SiO wherein thecoeificients A, B, C, D and B have the following numerical values:

A=50 to parts by weight 13:5 to 50 parts by weight C=0.75 to 1.0 moleD=0.05 to 0.25 mole E=2.5 to 5.5 moles Further, the concentration of thecoating composition should be such that the total solids of thecomposition should be about 30%40% by weight. The advantages of watersoluble coating having the polymers incorporated therein are shown bythe following specific examples which are given by way of illustrationand not as limitations on the scope of the present invention:

EXAMPLE l7 Lithium-s0dium silicate vehicle Grams Lithium hydroxidemonohydrate 62.0 Sodium hydroxide 20.0 Silica gel 270.0 Water 952.0

These ingredients were placed into a stainless steel pressure vesselunder continual agitation. The temperature was raised to C.; then thetemperature was gradually reduced to 25 C. over a period of 8 hours in amanner similar to Example 1.

Polyvinyl acetate component The Cellosize, a hydroxyethyl celluloseprotective colloid; Tergitol, an alkyl phenyl ether of polyethyleneglycol which acts as a surface active agent emulsifier; and potassiumpersulfate, used as a catalyst, are blended into the water in apolymerization reactor equipped with an agitator and a condenser. Thevinyl acetate and Z-ethylhexyl acrylate are combined and 10% by weightis added to the aqueous system. The aqueous system is warmed to 70 C.with agitation. The remaining vinyl acetate and Z-ethylhexyl acrylatemixture is added with stirring over a three-hour period maintaining thetemperature of the reaction at 7080 C. After the addition is complete,agitation is continued for one-half hour. The contents are then cooledto room temperature.

Coating composition Grams Lithium-sodium silicate vehicle 500 Polyvinylacetate emulsion 500 Iron oxide 50 Inert talc filler 200 The iron oxideand talc are dispersed in the vinyl acetate emulsion and the silicatesolution is then added. The coating mixture Was applied over ferrousmetal surfaces which had been wire brushed. Upon drying by waterevaporation, the coating exhibited excellent adhesion, hardness andmoisture resistance. It had an initial gloss of 30 as determined by a 60gloss meter, withstood a /s inch mandrel bend for flexibility and 8000scrub cycles in a 5% soap solution (ASTM D-16). The coating was notaffected after 96 hours exposure to 100% relative humidity at 40 C.

EXAMPLE 18 Another coating composition was prepared in the same manneras described in Example 17 but having the following composition:

A (emulsified polyvinyl acetate) +13 [(C Li O+D Na O) :E Si O] A=75parts by weight B=25 parts by weight C: 0.75 mole D=0.25 mole E=4.5moles Coating composition Grams Polyvinyl acetate emulsion 750Lithium-sodium silicate vehicle 250 Iron oxide 50 Inert talc filler 200This coating upon drying by Water evaporation exhibited the samesuperior adhesion and hardness properties as Example 17. It withstood anA; inch bend for flexibility and 6000 scrub cycles (ASTM D16).

EXAMPLE 19 A coating composition was prepared in the same manner asdescribed in Example 17 except it had the following composition:

A (polyvinyl acetate emulsion) +B [(C Li O+D Na O) :E Si O] A=100 partsB= part C=O part D=0 part E:O part Coating composition Grams Polyvinylacetate 1000 Iron oxide O Inert talc filler 200 This coating had pooradhesion and hardness. It exhibited blistering after 96 hours exposureto 100% relative humidity at 40 C. It withstood only 350 scrub cycles(ASTM D16).

8 EXAMPLE 20 Another coating composition was prepared in the same manneras described in Example 17 except it had the following composition:

A (polyvinyl acetate emulsion) +B [(C Li O+D Na O) :E Si O] A:0 part B=parts C=0.75 mol D=0.25 mol E=4.5 moles Coating composition GramsLithium-sodium silicate vehicle 1000 Iron oxide S0 Inert talc filler 200This coating was not completely satisfactory in that it became verybrittle and flaked from the surface. Further, it failed to produce acontinuous film. Although brittle, it exhibited excellent waterinsoluble properties.

EXAMPLE 21 Butyl rubber latex was pigmented and applied to a steel panelWhere it air dried with some corrosion of the steel. It had very pooradhesion and hardness. However, the addition of the lithium-sodiumsilicate as shown in the immediately following table resulted in a filmthat was superior in adhesion, hardness and flexibility.

Coating composition Grams Lithium-sodium silicate vehicle 250 Butylrubber latex, 54% solids 1000 Water 100 Talc-inert filler 200 Iron oxide50 From the foregoing examples, it can be seen that when the solution ofthe present invention is to be used on materials having a smooth, hardand non-porous surface, it finds its most effective utility as a liquidvehicle for specific additives which improve the adhesive and finishingqualities of the protective coating. Thus according to one aspect of thepresent invention, as illustrated heretofore, emulsified polymers suchas polyvinyl acetate, butyl rubber, and polyvinyl chloride may be mixedwith the liquid vehicle of the present invention.

Another important aspect of the present invention is to form adispersion of metallic dust in the aqueous lithium-sodium silicatesolution of the present invention. It has been found that the dispersionof a metallic dust, such as zinc, in the aqueous solution of the presentinvention, used as a liquid vehicle, and a small but effective amount ofan alkali metal dichromate provides a useful coating for protectingmetallic surfaces. Surprisingly, the coating provides protection fromcorrosion without contamination of hydrocarbons, aqueous solutions, andthe like, which may be in contact with the coated surfaces. Acomposition representing this aspect of the present invention is made inthe same manner as fully described in Example 1 except that after thesolution has cooled, a small but effective amount of an alkali metaldichromate, such as sodium or potassium dichromate, may be added. Afinely divided metal, such as Zinc dust, is then added to the cooledsolution in sufficient amounts to provide a protective surface when thecomposition is to be applied to exposed surfaces. Optionally, there maybe added to the cooled solution prior to, or simultaneously with thezinc dust an alkaline borate, iron oxide, sodium bicarbonate, and othermetals and compounds, if desired, which improve the characteristics ofthe protective metal coating when the solution is ap plied to an exposedsurface.

The finely divided metal is preferably zinc dust having a particle sizewithin the range from about 3 to about 25 microns; however, a preferredparticle size is within the range from about 6 to about microns. Withthe zinc dust may be used other metallic dusts, such as aluminum dust,magnesium dust, and selected metal oxide dust such as manganese dioxide,titanium dioxide, iron oxide and the like. It is preferred, however,that when other metallic ingredients are employed that the zinc dust beused in a major amount. Other materials such as sand and silica gel maybe employed, but it is to be emphasized that zinc dust is preferred,especially in protecting metallic surfaces. It has been found that whena small but effective amount of the metal oxides is used that thisimproves abrasion resistance, resistance to boiling water and hot saltwater spray and also improves the over-all general appearance of themetallic coating when applied to exposed surfaces.

It is emphasized that, in the practice of the present invention, thelithium and sodium silicates be employed in amounts suflicient toprovide a molar ratio of lithium oxide to sodium oxide to silicondioxide within the range from about 0.75 to about 1.00zabout 0.05 toabout 0.25:about 2.5 to about 5.0, respectively. A preferred ratio whena metallic dust is added is 0.8 of lithium oxide:0.2 of sodium oxide:4.5of silicon dioxide. The total Weight percent of the lithium hydroxideand sodium hydroxide in the solution having a metallic dust may rangefrom about 5.0 to about 15.0 percent. The amount of silica gel orsilicic acid may range from about 8 to about 25 percent by weight.

It is desirable in the practice of this aspect of the present inventionto-employ an alkaline borate in the composition inasmuch as the presenceof an alkaline borate, such as sodium borate, potassium borate, orammonium borate, greatly reduces or eliminates the friability of thefinal coating and allows the provision of a thicker coat than otherwisemight be obtained. An amount of the alkaline borate in the range from0.01 to about 0.20 percent by weight may be used. Thus,single-application compositions wherein the borate is not present andused to provide coatings having a thickness not greater than from about3 mils to about 6 mils, may have surface cracks rendering the coatingsunsuitable. Where an alkaline borate is present in the amount abovestated, however, a coating of at least 18 mils thickness may be obtainedwith no signs of surface cracking.

Also, when using metallic dust in the solution of the present invention,it is desirable to employ an alkaline bicarbonate, such as sodium orammonium bicarbonate. The presence of this material improves the waterinsolubility and accelerates the self-curing or air-cur ingcharacteristics of the coating. Where an alkaline bicarbonate isemployed, it may be present in an amount in the range from about 0.01 toabout 0.20 percent by weight.

An important feature of the present invention when preparing a coatingfor a metallic surface is the presence of an oxidizing agent, such as analkaline dichromate as exemplified by potassium dichromate or sodiumdichromate. The presence of the oxidizing agent increases the useable orpot life of the coating material after metal dust and the liquid vehiclehave been admixed. For example, by dissolving 0.05 to 0.10 percent byweight of potassium dichromate in the liquid vehicle, the useful life ofthe coating mixture is substantially lengthened.

The composition of this aspect of the present invention may be made upas follows:

EXAMPLE 22 A stainless steel autoclave suitably equipped with a stirringdevice and capable of withstanding an internal autogenous pressure of atleast 600 p.s.i., and equipped with a heating device such that thecontents may be heated to about 150 C. is provided. The autoclave ischarged with 400 parts by weight of water and the stirring device isplaced in operation. About 34 parts of lithium hydroxide containing 1molecule of water and 8 parts of sodium hydroxide are added to the waterin the autoclave and stirred from about 5 to about 10 minutes.Thereafter, about 126 parts of silica gel are added. Silicic acid may besubstituted for the silica gel, but it will be necessary to adjust theamount thereof because of the presence of the water of hydration. Theautoclave is then closed and stirring is continued and it is then heatedto a temperature within the range indicated, preferably about to aboutC. The temperature of the contents of the autoclave is brought up to themaximum temperature over a period of about 30 minutes, and thereafterthe temperature is slowly reduced to a temperature of about 20 to about30 C., preferably about 25 C., over a period up to about 6 hours.Stirring may then be continued for an additional period of time up toabout 14 hours, at which time there is added to the contents of theautoclave about 0.05 percent by weight of an alkaline dichromate, suchas potassium dichromate. An alkaline borate, such as sodium borate, inan amount of about 0.02 percent by weight and an alkaline bicarbonate,such as sodium bicarbonate in an amount of about 0.15 percent by weightmay also be added. Stirring is continued until a complete solution iseffected, which may be for about 10 minutes. This provides asingle-application coating composition, and the composition is suitablefor immediate use. To the liquid composition is then added about 300parts of zinc dust for every 100 parts of the composition as describedabove. This composition may then be applied to a freshly sandblastedsurface, such as a metallic surface as exemplified by steel, and allowedto dry by exposure to the atmosphere for about one hour.

At this point, it should be emphasized that compositions made up simplyby mixing the several ingredients at ambient temperatures with stirringdo not produce satisfactory coating compositions. For example, a coatinginferior in quality to that produced in accordance with the presentinvention is produced when the ingredients are simply mixed together.

In order to illustrate that lithium and sodium silicates must be presentin this aspect of the present invention, the following compositions aremade up:

EXAMPLE 23 Sodium silicate is employed in this composition in a molarratio of 3.22 of silicon dioxide to sodium oxide at 30 percent solids byweight employing 0.05 percent potassium dichromate. This aqueoussolution is mixed at a 3:1 weight ratio using zinc dust having aparticle size of 10 to 12 microns. When this composition is applied to asandblasted steel panel and allowed to air dry one hour and then exposedto boiling water for 5 minutes, the coating is completely destroyed.

EXAMPLE 24 In another composition, a molar ratio of 4.5 :1 of silicondioxide to lithium oxide is employed at 26-27 percent solids by weightand the aqueous solution mixed at a 3:1 weight ratio using zinc dusthaving a particle size of 10 to 12 microns. Application of thiscomposition to a sandblasted steel panel indicates unsatisfactoryresults when allowed to dry in air one hour and then exposed to boilingwater for one hour. Thus, the coating is insoluble but exhibitsexcessive friability. The initial hardness of the coating is inadequate.

EXAMPLE 25 A similar composition is also made, except that zinc dusthaving a particle size of 3 to 5 microns is employed. On application ofthe resulting mixture to a sandblasted steel panel and drying for onehour, then exposing to boiling Water for one hour, the coating is foundinsoluble, but exhibits friability. The initial hardness of the coatingis adequate, but the film thickness is insuflicient in that surface ormud cracking is observed.

EXAMPLE 26 Thereafter, a composition in accordance with the presentinvention was made wherein silicon dioxide to total lithium and sodiumoxides in a molar ratio of 4.5:1.0 was prepared. In this instance, theratio of lithium oxide to sodium oxide was 3:1. Potassium dichromate inan amount of 0.05 percent by weight was mixed with zinc dust, the zincbeing employed in a ratio of 3 parts zinc to 1 part of solution. Theresulting composition was applied to a sandblasted steel panel andallowed to dry in air for one hour and then exposed to boiling water forone hour. This composition exhibited unusual water insolubility and nofriability was observed. Moreover, the initial hardness of the coatingwas greater than the corresponding lithium silicate composition.

EXAMPLE 27 The same composition was again prepared as in Example 26except that zinc dust having a particle size of 3 to microns wasemployed. When dried in air for one hour and exposed to boiling waterfor one hour, the composition again displayed unusual waterinsolubility, no friability and had extreme initial hardness.

EXAMPLE 28 Another composition wherein silicon dioxide to total lithiumand sodium oxides in a molar ratio of 4.5 to 1.0 was prepared. In thisinstance, the ratio of lithium oxide to sodium oxide was 4:1. Potassiumdichromate in an amount of 0.05 percent by weight was mixed with thealkali silicate solution. The zinc dust, having an average particle sizeof 7 to 9 microns, was employed in a ratio of 3 parts of zinc to 1 partof solution. The resulting composition was applied to a sandblastedsteel surface and allowed to air dry for one hour, then exposed toboiling water for one hour. The composition exhibited unusual waterinsolubility and no friability was observed. The initial hardness of thecoating was 8H as determined by standard pencils and it withstood 5 to 6percent elongation upon being impacted with 13.4 foot pounds of force.Also, the resulting coating withstood one thousand hours exposure to 5%warm salt spray and one thousand hours exposure to 100 percent relativehumidity at 40 C. without failure. The abrasion resistance of thecoating, as determined by a Taber abraser, was outstanding and required10,000 cycles to destroy 1 mil thickness of the coating. Adequate filmthickness of 12-14 mils could be applied without surface cracking.

EXAMPLE 29 The same composition was again prepared as in Example 28except that zinc dust having a particle size of 12 microns was employed.The resulting coating after air drying one hour exhibited the sameunusual water insolubility, but had a soft, less abrasive resistantfilm. Only 6000 cycles on the Taber abraser was required to destroy onemil thickness of the film and the pencil hardness was 6H+. However, tomil film thicknesses could be applied without surface cracking andflaking of the coating.

EXAMPLE 3 0 Another composition wherein silicon dioxide to total lithiumand sodium oxides in a molar ratio of 45:10, was prepared. In thisinstance, the ratio of lithium oxide to sodium oxide was 1:1. Potassiumdichromate in an amount of 0.05 percent by weight was mixed with thealkali silicate solution. The zinc dust having an average particle sizeof 7 to 9 microns was employed in a ratio of 3 parts of zinc to 1 partof solution. The resulting composition was applied to a sandblastedsteel surface and allowed to air dry for one hour, then exposed toboiling water for 30 minutes at which time, the coating was destroyed.The initial hardness of the coating was 8H+ as determined by standardpencils and withstood 5 to 6 percent elongation upon being impacted with13.4 foot pounds of force. Also, the resulting coating exhibited percentfailure after being exposed for only one hundred and fifty hours in 5%warm salt spray and 80% failure after exposure of three hundred hours torelative humidity at 40 C. However, thick films of 20 mils could beapplied Without surface cracking.

EXAMPLE 3 1 Another composition wherein silicon dioxide to total lithiumand sodium oxides in a molar ratio of 4.5 to 1.0, was prepared. In thiscomposition, the ratio of lithium oxide to sodium oxide was 9:1.Potassium dichromate in an amount of 0.05 percent by weight was mixedwith the alkali silicate solution. The zinc dust having an averageparticle size of 10 to 12 microns was employed in a ratio of 3 parts ofzinc to 1 part solution. The resulting composition was aplied to asandblasted steel surface and allowed to air dry for one hour, thenexposed to boiling water for one hour. The composition exhibited goodwater insolubility and very slight friability. The initial hardness ofthe coating was 6H as determined by standard pencils, and it withstood 5to 6 percent elongation upon being impacted with 13.4 foot pounds offorce. It passed a one-half inch mandrel bend for flexibility, butrequired only 6000 cycles on the Taber abraser to destroy one mil ofcoating thickness. Films of 15 to 16 mils could be applied withoutsurface cracking or flaking of the coating.

EXAMPLE 32 The same composition was again prepared as in Example 31except that zinc dust having a particle size of 7 to 9 microns wasemployed. The resulting coating after air drying one hour exhibitedunusual water insolu bility and excellent initial hardness of 6H+. Eightthousand cycles on the Taber abraser was required to destroy one mil ofcoating film, and it withstood 5 to 6 percent elongation upon beingimpacted with 13.4 foot pounds of force. Adequate film thickness of 10to 12 mils can be applied Without surface cracking and flaking.

In the foregoing compositions, reference is had to solids content. Inthe practice of .the present invention, the total solids contained inthe liquid composition should be in the range of about 24 to about 31percent by weight as determined by heating a weighed quantity of theliquid composition at C. for two hours and then weighing to determinethe percent of solids.

The liquid composition in accordance with the present invention which isexclusive of the metallic dust and other additives was made upindicative of a commercial scale to consist essentially of thefollowing.

Components: Pounds Sodium hydroxide 3.75 Lithium hydroxide monohydrate11.75 Silica gel 50.50 Water 178.00 Potassium dichromate 0.122

The several components, excepting the potassium dichromate, werecharged, in the order shown, into a stainless steel pressure vesselequipped with an agitator. The mixture increased in temperature from 25C. to 50 C. by evolution of exothermic heat. The vessel was then sealedand the temperature and pressure of the contents under continualagitation were raised to C. and 60 pounds per square inch within 30minutes. When the temperature reached 150 C., the contents of the vesselwere slowly cooled at an average rate of 034 C. per

to the solution under vigorous agitation. the chromate was completelydissolved, the finished lithium-sodium silicate was withdrawn from thevessel. 7

In employing the present invention, a useful protective coating mixtureis provided by mixing a finely divided metal, such as a mixture of Zincor aluminum dust, with alkaline dichromate and optional ingredients witha liquid composition containing lithium and sodium silicates in a weightratio of about 2:1 to about 4:1 of a metallic dust to liquid vehicle.The coating mixture is applied to 'a freshly sandblasted metal surface,such as steel or other metals, by spray, brush, roller or dipping andallowed to dry in the air. The resulting coating is abrasive resistant,withstands the action of boiling water for eight hours, withstands hotsalt water spray for several weeks, and provides a superior coatingcomposition. In testing the steel panels, the coating was sprayed on afreshly sandblasted piece of /s-incl1 thick steel plate four inches wideand four inches long. The test panels on which the coating was sprayedwere air dried at about 25 C. for one hour and then subjected tophysical testing, such as immersion in boiling water, exposure to a 5percent heated salt-water spray for periods up to one thousand hours,exposure to 100 percent relative humidity at a temperature of 38 to 40C. for a period of one thousand hours and exposure to hot liquidhydrocarbons. The hardness of the coating was determined by the use ofstandard pencils of various hardness ratings. Abrasion resistance wasalso employed as an indication of the hardness of the coating asdetermined by the Taber abraser with a CS-17 abraiding wheel and 1000gram load. Flexibility was determined by a 90 bend of a test panel onwhich the coating was applied and by impact of a coated panel with 13.4foot pounds force.

The nature and objects of the present invention having been completelydescribed and illustrated and the best mode thereof set forth, what wewish to claim as new and useful and secure by Letters Patent is:

1. A method for preparing a mixed lithium-sodium silicate solutioncomprising admixing lithium hydroxide, sodium hydroxide, asilica-containing material selected from the group consisting of silicagel and silicic acid, and water, while agitating same; heating saidadmixture while continuing the agitation thereof to a temperature withinthe range from about 75 to about 150 C. for a sufficient length of timeto form an admixture of lithium and sodium silicates; said lithium andsodium hydroxides and silica-containing material being employed inamounts sufficient to provide a ratio of lithium oxide to sodium oxideto silicon dioxide within the range from about 0.75 to about 1.00 LiO:about 0.05 to about 0.25 Na O: about 2.5 to about 5.0 SiO and a totalsolids from about percent to about 45 percent by weight; and coolingsaid admixture to a temperature within the range from about 20 to about30 C. to form an aqueous solution thereof.

2. A composition of matter comprising an aqueous solution of a mixtureof lithium silicate and sodium silicate made by the method of claim 1wherein said lithium and sodium hydroxides and silica-containingmaterial are employed in amounts to produce a total solids of 24 percentto 31 percent by Weight.

3. Glass matting impregnated with an aqueous solution of a mixture oflithium silicate and sodium silicate, said lithium silicate and saidsodium silicate being employed in amounts sufficient to provide a molarratio of lithium oxide to sodium oxide to silicon dioxide within therange from about 0.75 to about 1.00 Li O:about 0.05 to about 0.25 NaOzabout 2.5 to about 5.0 SiO and a total solids of 24 percent to 31percent by weight.

4. Woven roving impregnated with an aqueous solution of a mixture oflithium silicate and sodium silicate,

said lithium silicate and said sodium silicate being employed in amountssufficient to provide a molar ratio of lithium oxide'to sodium oxide tosilicon dioxide within the range from about 0.75 to about 1.00 LiO:about 0.05 to about 0.25 Na O:2.5 to about 5.0 SiO and a total solidsof 24 percent to 31 percent by weight.

5. Insulation material impregnated with an aqueous solution of a mixtureof lithium silicate and sodium silicate, said lithium silicate and saidsodium silicate being employed in amounts sufficient to provide a molarratio of lithium oxide to sodium oxide to silicon dioxide within therange from about 0.75 to about 1.00 Li ozabout 0.05 to about 0.25 Naozabout 2.5 to about 5 .0 SiO and a total solids of 24 percent to 31percent by weight.

6. Paper fibers impregnated with an aqueous solution 7 of a mixture oflithium silicate and sodium silicate, said lithium silicate and saidsodium silicate being employed in amounts sufficient to provide a molarratio of lithium oxide to sodium oxide to silicon dioxide within therange from about 0.75 to about 1.00 Li Ozabout 0.05 to about 0.25 Na ozabout 2.5 to about 5.0 SiO and a total solid of 24 percent to 31percent by weight.

7. Wood impregnated with an aqueous solution of a mixture of lithiumsilicate and sodium silicate said lithium and said sodium silicate beingemployed in amounts sufficient to provide a molar ratio of lithium fromabout 0.75 to about 1.00 Li O:about 0.05 to abou 0.25 Na ozabout 2.5 toabout 5.0 SiO and a total solids of 24 percent to 31 percent by weight.

8. An adhesive composition comprising an aqueous solution of a mixtureof lithium silicate and sodium silicate, said lithium silicate and saidsodium silicate being employed in amounts sufficient to provide a molarratio of lithium oxide to sodium oxide to silicon dioxide in the rangefrom about 0.75 to about 1.00 Li O:about 0.05 to about 0.25 Na O:about2.5 to about 5.0 SiO and a total solids of 24 percent to 31 percent byweight; a filler material selected from the group consisting of casein,clay, sugar, aluminate, and asbestos present in an amountlbetween 5percent and percent by weight; and curing agent selected from the groupconsisting of bor x, potassium chloride, and potassium bromide, presentin an amount between 0.01 percent and 3.0 percent by weight.

9. A composition of claim 8 wherein the filler is clay and the curingagent is borax.

10. A composition of claim 8 wherein the filler is clay and makes upabout 5% to about 20% by weight of said composition and the curing agentis borax and makes up about 0.2% by weight of said composition.

11. A water-soluble coating composition comprising an aqueous solutionof a mixture of lithium silicate and sodium silicate, said lithiumsilicate and sodium silicate being employed in amounts suflicient toprovide a molar ratio of lithium oxide to sodium oxide to silicondioxide within the range from about 0.75 to about 1.00 Li O: about 0.05to about 0.25 Na O:about 2.5 to about 5.0 SiO and a total solids fromabout 10 percent to about 45 percent by weight; and emulsified polymerselected from the class consisting of polyvinyl acetate,polyvinylchloride, and butyl rubber; said solution of lithium silicateand sodium silicate being in the range of about 5 to 50 parts by weight,and the emulsified polymer being in the range of about 50 to parts byweight.

12. A water soluble coating composition according to claim 11 whereinthe emulsified polymer is polyvinyl acetate.

13. A water-soluble coating composition comprising a lithium-sodiumsilicate vehicle consisting of a mixture of lithium silicate and sodiumsilicate, said lithium and sodium silicate being employed in amountssufficient to provide a molar ratio of lithium oxide to sodium oxide tosilicon dioxide within the range from about 0.75 to about 1.00 Liozabout 0.05 to about 0.25 Na ozabout 2.5 to about 5.0 Si0 and a totalsolids from about 10 percent to about 45 percent by weight, said vehiclebeing present in an amount between 50 to 100 parts by weight; apolyvinyl acetate emulsion present in an amount between 5 to 50 parts byweight; iron oxide present in about 5 parts by weight and inert talcfiller present in about 20 parts by weight.

14. A water-soluble coating composition according to claim 13 whereinsaid lithium silicate and sodium silicate are employed in amountssuflicient to provide a molar ratio of about 0.75 Li ozabout 0.25 NaOzabout 4.5 Si and a total solids of 24 percent to 31 percent by weight.

15. A single-application coating composition comprising lithium silicateand sodium silicate, said lithium silicate and said sodium silicatebeing employed in amounts suflicient to provide molar ratio of lithiumoxide to sodium oxide to silicon dioxide within the range from about0.75 to about 1.00 Li ozabout 0.05 to about 0.25 Na ozabout 2.5 to about5.0 SiO and a total solids of 24 percent to 31 percent by weight, and analkali metal dichromate in an amount from about 0.05 to about 0.10percent by weight.

16. A single-application liquid coating composition comprising adispersion of zinc dust in an amount sulficient to provide a protectivecoating on metallic surfaces protected by zinc in an aqueous solution ofa mixture of lithium silicate and sodium silicate, said lithium silicateand said sodium silicate being employed in amounts sufiicent to providea molar ratio of lithium oxide to sodium oxide to silicon dioxide withinthe range from about 0.75 to about 1.00 Li Ozabout 0.20 to about 0.25 NaO:about 4.5 SiO and a total solids of 24 percent to 31 percent by weightand an alkali metal dichromate in an amount from about 0.05 to about0.10 percent by weight.

17. A composition in accordance with claim 16 in which the zinc dust hasa particle size within the range of about 3 to 25 microns.

18. A composition in accordance with claim 16 in which the particle sizeof said zinc dust is within the range from about 6 to about 10 microns.

19. A method for preparing a liquid vehicle for a single-applicationcoating composition which comprises admixing lithium hydroxide, sodiumhydroxide, and a silicacontaining material selected from the groupconsisting of silica gel and silicic acid, and water while agitatingsame; heating said admixture while continuing the agitation thereof to atemperature within the range from about 75 to about 150 C. for asufiicient length of time to form an admixture of lithium and sodiumsilicates; said lithium and sodium hydroxides and silica-containingmaterial being employed in amounts sufficient to provide a ratio oflithium oxide to sodium oxide to silicon dioxide within the range fromabout 0.75 to about 1.00 Li ozabout 0.05 to about 0.25 Na O:about 2.5 toabout .0 SiO and a total solids from about percent to about 45 percentby weight; cooling said admixture to a temperature within a range fromabout 20 to about 30 C. to form an aqueous solution thereof; and thenadding to said cool solution an amount from 0.05 to 0.10 percent weightof an alkali metal dichromate.

20. A method for preparing a liquid vehicle for a single-applicationcoating composition which comprises admixing lithium hydroxide, sodiumhydroxide, a silicacontaining material selected from the groupconsisting of silica gel and silicic acid and water, while agitatingsame; heating said admixture while continuing the agitation thereof to atemperature within the range from about 75 to about 150 C. for asufiicient length of time to form an admixture of lithium and sodiumsilicates; said sodium and lithium hydroxides and silica-containingmaterial being employed in amounts sufiicient to provide a ratio oflithium oxide to sodium oxide to silicon dioxide within the range fromabout 0.75 to about 1.00 Li ozabout 0.05 to about 0.25 Na Ozabout 2.5 toabout 5.0 $0 and a total solids from about 10 percent to about 45percent by weight; cooling said admixture to a temperature within therange from about 20 to about 30 C. to form an aqueous solution thereof;and then adding to said co'ol solution an amount from about 0.05 toabout 0.10 percent by Weight of an alkali metal dichromate and analkaline borate selected from the group consisting of sodium borate andammonium borate in the amount of about 0.01 to about 0.20 percent byweight.

21. A method for preparing a single-application coating compositionwhich comprises admixing lithium hydroxide, sodium hydroxide, and asilica-containing material selected from the group consisting of silicagel and silicic acid, and water, while agitating same; heating saidadmixture while continuing the agitation thereof to a temperature withinthe range from about 75 to about 150 C. for a sufiicient length of timeto form an admixture of lithium and sodium silicates; said sodium andlithium hydroxides and silica-containing material being employed inamounts sufficient to provide a ratio of lithium oxide to sodium oxideto silicon dioxide within the range from about 0.75 to about 1.00 Liozabout 0.05 to about 0.25 Na Ozabout 2.5 to about 5.0 Si0 and a totalsolids from about 10 percent to about 45 percent by weight; cooling saidadmixture to a temperature within the range from about 20 to about 30 C.to form an aqueous solution thereof; adding to said cool solution asmall but effective amount of an alkali metal dichromate to extend thepot-life upon addition of zinc dust; and adding to said solution asufiicient amount of zinc dust to provide a protective coating onexposed metallic surfaces protected by zinc.

22. A method in accordance with claim 21 in which the zinc dust has aparticle size within the range from about 6 to about 25 microns.

23. A method in accordance with claim 21 in wh ch the particle size iswithin the range from about 6 to about 10 microns.

24. A single-application coating composition consisting essentially of adispersion of about 3 parts by weight of zinc dust in 1 part by weightof an aqueous solution of a mixture of lithium silicate and sodiumsilicate, said lithium silicate and said sodium silicate being employedin amounts sufiicient to provide a molar ratio of lithium oxide tosodium oxide of about 3:1 and a molar ratio of silicon dioxide to thecombined lithium oxide and sodium oxide of about 4.521 and potassiumdichromate in an amount of about 0.05 weight percent of said aqueoussolution.

25. A composition in accordance with claim 24 in which the zinc dust hasa particle size within the range of about 3 to 25 microns.

26. A method for preparing a liquid vehicle for a singleapplicationcoating composition which comprises admixing lithium hydroxide, sodiumhydroxide, a silica-containing material selected from the groupconsisting of silica gel and silica acid and water, while agitatingsame; heating said admixture while continuing the agitation thereof to atemperature of about to about C. for a sufficient length of time to forman admixture of lithium and sodium silicates; said lithium and sodiumhydroxides and silica-containing material being employed in amountssufiicient to provide a ratio of lithium oxide to sodium oxide tosilicon dioxide Within the range from about 0.75 to about 1.00 LiO:about 0.05 to about 0.25 Na ozabout 2.5 to about 5.0 SiO and a totalsolids from about 10 percent to about 45 percent by weight; cooling saidadmixture to a temperature of about 95 C. at a rate within the range ofabout 0.61 C. to about 1.83 C. per minute, and thereafter cooling saidadmixture at a slower rate to a temperature within a range from about 20to about 30 C. to form said liquid vehicle.

27. A method in accordance with claim 26 wherein said lithium and sodiumhydroxides and silica-containing material are employed in amounts toproduce a total solids of between 24 percent and 31 percent by weight.

28. A method in accordance with claim 26 wherein said lithium and sodiumhydroxides and silica-containing material are employed in an amount toprovide a ratio of lithium oxide to sodium oxide to silicon dioxide ofabout 0.75 Li ozabout 0.25 Na ozabout 4.5 Si0 and a total solids ofbetween 24 percent and 31 percent by weight.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCESMellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry,published by Longmans, Greer and Co., London, 1925, vol. 6, page 329.

Soluble Silicates in Industry, Vail, The Chemical Catalog Company Inc.,New York, 1928, page 70.

T OBIAS E. LEVOW, Primary Examiner.

JOSEPH REBOLD, Examiner.

1. A METHOD FOR PREPARING A MIXED LITHIUM-SODIUM SILICATE SOLUTIONCOMPRISING ADMIXING LITHIUM HYDROXIDE, SODIUM HYDROXIDE, ASILICA-CONTAINING MATERIAL SELECTED FROM THE GROUP CONSISTING OF SILICAGEL AND SILICIC ACID, AND WATER, WHILE AGITATING SAME; HEATING SAIDADMIXTURE WHILE CONTINUING THE AGITATION THEREOF TO A TEMPERATURE WITHINTHE RANGE FROM ABOUT 75* TO ABOUT 150*C. FOR A SUFFICIENT LENGTH OF TIMETO FORM AN ADMIXTURE OF LITHIUM AND SODIUM SILICATES; SAID LITHIUM ANDSODIUM HYDROXIDES AND SILICA-CONTAINING MATERIAL BEING EMPLOYED INAMOUNTS SUFFICIENT TO PROVIDE A RATIO OF LITHIUM OXIDE TO SODIUM OXIDETO SILICON DIOXIDE WITHIN THE RANGE FROM ABOUT 0.75 TO ABOUT 1.00 LI2/:ABOUT 0.05 TO ABOUT 0.25 NA2O: ABOUT 2.5 TO ABOUT 5.0 SIO2, AND A TOTALSOLIDS FROM ABOUT 10 PERCENT TO ABOUT 45 PERCENT BY WEIGHT; AND COOLINGSAID ADMIXTURE TO A TEMPERATURE WITHIN THE RANGE FROM ABOUT 20* TO ABOUT30*C. TO FORM AN AQUEOUS SOLUTION THEREOF.